In an engine of an automobile vehicle, in order to reduce the NOx contained in the exhaust gas thereof, is provided an exhaust gas recirculation apparatus recirculating the exhaust gas to the intake side thereof. The exhaust gas recirculation passage is provided with an EGR valve (“Exhaust Gas Recirculation” valve), and the EGR valve is opened or closed by control based on the driving information or the like of the engine. If high-temperature exhaust gas is recirculated to the intake side as it is, the efficiency thereof becomes deteriorated, and the high-temperature exhaust gas has an adverse effect on the EGR valve. Thus, the exhaust gas recirculation passage is provided with an EGR cooler for cooling the high-temperature exhaust gas.
Exhaust gas passing through an EGR valve contains sulfur oxides coming from a fuel system, and nitrogen oxides and particulate matter (PM) such as soot and the like which are produced by combustion. Therefore, those substances are also introduced in the exhaust gas recirculation passage, and they adhere to a valve rod of the EGR valve. When the soot and the like are deposited over the valve rod (the matter deposited thereover is referred to as “deposit”), they can cause trouble in normal operation of the valve rod. In order to solve the troubles caused by the adhesion of the particulate matter to the valve rod, a technology is disclosed, in which a first sleeve enclosing a valve rod is provided integral with a valve disk provided at the tip of the valve rod and further a second sleeve located within the first sleeve is provided on the housing side (Patent Document 1).
Patent Document 1: JP-A-2002-285918
However, the technology disclosed in Patent Document 1 requires that the valve disk have a special shape in order to attach the first sleeve thereto. Further, it is necessary to install the first sleeve on the valve disk separately from the installation of the valve disk on the valve rod, resulting in increasing one manufacturing step.
The present invention has been accomplished to solve such a technical situation, and an object thereof is to provide a structure in which a cover enclosing a valve rod of an EGR valve can be manufactured in a more compact structure and in a simpler process.